A variety of control units have been employed for controlling automotive heating, ventilating and air conditioning systems. Typically, a control unit includes a single movable function control member, such as a lever or slider, having a multiplicity of positions, corresponding with the desired functional modes of operation. In a typical control unit, the multiposition lever or slider operates both a multiposition vacuum control valve and one or more electrical switches. The switches may control the energization of a blower motor and an air conditioning clutch, whereby an air conditioning compressor is driven. The multiposition vacuum control valve supplies intake manifold vacuum to various vacuum motors for operating doors or valve plates in the air duct system, for controlling the movement of air to and from the desired locations in the system.
In addition to the function control unit, there is usually a heat control, which may be in the form of a movable lever or slider, for regulating the amount of heat supplied by the system, and a multiposition blower speed control switch, for regulating the speed of the blower motor.
The typical control unit, having a single function control lever or other member, suffers from the disadvantage that some drivers find it difficult to adjust the lever to the desired position, without being unduly distracted from the primary task of driving the vehicle. While the typical control unit has a detent mechanism for detaining the control lever in the desired positions, the lever can also be adjusted to ambiguous positions, between the various detented positions.